Hi there

I hope you are still healthy. Because of Covid-19 pandemic I developed this printable mask. You can print it without supports and it takes about 5 hours to print all parts if you print it with 0.2 layers and 0.6 nozzle. I used a PET-G material for it. This material is easy to clean and disinfect. To print this mask you have to use smooth bed sheet so the ventile membrane can seal properly to the mask. Do not use textured powder-coated bed sheet.

This mask is suitable for not too skinny face and size is somewhere in the middle. The good sealing is achieved only with your thicker face skin and if you’re shaved. Tested on my face. I am a man 173 cm height (5'-8") 70 kg weight.

Filter
As a filter I used cosmetic cleaning pads made from 100% cotton which are 6 cm in diameter. They can be bought in a drugstore. You can replace them easy from inner side of the mask every day or more frequently. There is a removable grid inside the mask holding the pad in place.

Exhalation Valve
As a ventil membrane I cut a 3cm disk from 0.2 mm thick sheet of i guess polypropylene (not sure what material it is). Basically it was an alphabetic divider sheet from business card book i found home. Use something similarly thin flexible but with shape memory. Paper or fabric is not suitable and tends to lose sealing quality because of getting wet while breathing out. There is a disc template you can print for an easier marking the size and center on the sheet.
Edit-1: I tried to print this disk and it works perfectly. It should be one 0.2 mm layer, 30 mm in diameter and central hole is 4.6 mm in diameter. You need to use Cutter Knife (flatwise) to carefully remove it from the smooth bed sheet. When assemble, pay attention to correct orientation of the printed disk. Smooth side towards the mask to establish good sealing. I added STL file with the disk.
Edit-2: The Exhalation Valve can be a potential risk for the spread of the virus if you are already infected. But it is questionable if the leaks through or over the edges of the homemade or disposable mouth drapes are similar like through the valve.
Edit-3: I found that there was no 100% exhalation through the valve. It only works as a help and part is exhaled through the filter.

Straps
As a strap I used rubber bought in haberdashery. They only had 16mm wide in my case. Use whatever you find comfortable and available.

The most challenging part was to find out the ventil mechanism (but finally i copied the principal from existing ones) and design all parts to be printable without supports and easy to assemble without need of any screws or gluing and keep nice aesthetic.
The last wish is to find better and comfortable sealing to the face using available items you can find home or to buy in available stores (most stores are closed during pandemic).

Post-Printing
Use sand paper or knife to remove hard edges and filament excesses where needed.

Room for improvement:

• better and comfortable sealing to the face using kind of silicone seals e.g. like swimming goggles
• strap fastening
• ventil membrane material options (solved)
• filter material options

NOTE:
This mask is just an attempt to protect myself and close ones anyhow possible. This mask is not certified as an medical aid and can not be used as an replacement. Consider all facts and use it on your risk. I can not 100% guarantee this mask will protect you but I believe better is something then nothing. I disclaim any responsibility for misuse or wrong use of the mask.

Here is an article about DIY masks and proper filter materials and its effectiveness:
https://smartairfilters.com/en/blog/best-materials-make-diy-face-mask-virus/

A feedback, comment or like is always welcome!

Share with me how this product helps you, how you use it or why you like it or not.
What is your story with this product?

Happy printing and stay healthy.

Revisions
22.03.2020
Updated print file - lower the print time
I added STL for ventile membrane

Print instructions

Material: PET-G
Nozzle: 0.6
Layer height: 0.2
Perimeters: 3
Top Layers: 6
Bottom Layers: 5
Infill: Grid 30%
Bed sheet: Smooth! (so the ventile membrane can seal properly to the mask)